Rotary hammers are known in which a motor drives a spindle supporting a hammer bit, while at the same time causing a piston tightly fitted within the spindle to execute linear reciprocating motion within the spindle. This motion causes repeated compression of an air cushion between the piston and a ram slidably mounted within the spindle, which causes the ram in turn to execute reciprocating linear motion within the spindle and apply impacts to the hammer bit via a beat piece.
In know designs of rotary hammer, the piston is reciprocatingly driven by the motor via a wobble bearing or crank. However, such designs typical require a large amount of space for such drive systems in relation to the amount of reciprocating movement of the piston.
Further, rotary hammers of this type suffer from the drawback that in order to generate an air cushion between the piston and the ram, the external dimensions of the piston and ram must be closely matched to the internal dimensions of the spindle, which increases the cost and complexity of manufacture of the hammer.
The present invention seeks to overcome or at least mitigate some or all of the above disadvantage of the prior art whilst producing a compact design.
US6199640 is a relevant piece of prior art known to the applicant.